If we go still farther into details, the results will be found startling enough. Let us select one of the periods, the old red sandstone, for illustrating our views. The period assigned for this formation embraces a term of about, we shall suppose, according to the geological distribution of time, a million or two of years. This formation consists of three great subdivisions, every one of which contains their distinct specific forms, and hence their separation into the lower, middle, and upper groups. This was pre-eminently the fish epoch—finners which roamed in undisturbed possession of every sea on the surface of the globe. Dropping into the waters, and speedily silted up in the sands, the skeletons were in the best of all possible circumstances for preservation; and accordingly, the specimens of the period constitute the wonder of the geologist, for their enameled freshness and perfect outline of figure. The productiveness of fish is prodigious, the cod-fish multiplying at the rate of three millions and a-half, mackerel at about half a million, and most of the other tribes at a corresponding high ratio. Count now how many generations, of every one of the species of the separate groups of the old red sandstone series, would exist and multiply during a period of so many hundred thousand years. The modern epoch and its breeders have scarcely reached their six thousand. When six times six have been added, and sixty times more have been added to these, they will still be a third short of the term allotted to the favored denizens of the olden time. And where, amidst the well-protected few that have yielded up their remains, are the traces of the myriads upon myriads that perished and were buried along with them? To the genus Homo, the head of creation, few think of the earth, as it now is, being the abode for periods reckoned by millions of years. Nay, within his as yet brief period, how many of his cotemporaries have already passed from the stage, extirpated, many of them, by his own direct agency? The dodo, and his fellow islander the solitaire, and other brevipennate birds,—probably, too, the elk and the urus,—certainly from this island the beaver, the wolf, and the bear, and just as certainly, at no distant day, the extinction of many other races will follow in the onward progress of civilization. But as now, so in all past ages, superior power, or a more dextrous instinct, have led to their extirpation. Their destiny was fulfilled, and the race perished. And as we are reasoning upon the known laws of nature, whence the geologist only seeks a footing for his vast cycles of time, so, we venture to affirm, is he bound to abide by the test of his own selection, and to read therein the terms of life granted to the families of earth. The modern epoch shows the outgoing of genera as well as of species within the limited compass of a few thousand years—gives reasonable indications of the